# Gravity

If you've ever thrown loose change into a [spiral wishing
well](https://www.spiralwishingwells.com/), then you've paid a small price to
see an invisible force with your own eyes. Gravity is responsible for the
formation of stars, the motion of planets, and 100% of hoverboarding accidents.

Gravity also explains how members orbit a community. They pull themselves toward
the community voluntarily, drawn in by an alignment to the mission, a sense of
value for themselves, and relationships with other members.

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## What is gravity?

In the Orbit Model, gravity isn't just a theory, it's something that we define
and calculate.

> Gravity is defined as **the rate at which member involvement is
> changing**.

When gravity is high, new members become involved, active members become leaders, and so on — all at a faster rate as compared to lower gravity communities.

Gravity is measured at the overall community level. At the individual level, we can measure a person's [love](./love), which we'll explore in a later section.

## Comparing gravity: an example

_Alice_ recently joined a community that hosts weekly events. She's been
getting a lot of value out of the events, and she's returning every week.
Soon she plans to volunteer to help host an event.

_Laura_ recently joined a different community. She found the first few events to
be interesting but didn't meet anyone she really connected with. As a result,
Laura's only attending a community event about once a month, and isn't interested in helping host.

Assuming we have no other information, we can say that Alice's community has a
higher gravity than Laura's. If we looked at the participation rate and roles of
_all_ members in each community, we could compare the two holistically.

In this example, it's possible that Alice's community is great at getting new members involved, but Laura's is better at turning highly engaged members into leaders.

Every community has a unique field of gravity, with different strengths at each level.

## Gravity as a metric

Before we dive into the specifics calculating gravity, let's talk about why our definition makes sense.

> A good metric doesn't need to paint an exact picture of the world, it's more
> **important that the metric incentivizes the _right behavior_ to influence it**.

Based on the thousands of communities we've worked with, measuring member involvement seems to lead to the right actions for both the members, the overall community, and the business behind the community, if there is one.

Everyone wins when the rate of member participation is increasing.

Measuring gravity in this way encourages community builders to define what commitment means and create ways to move members to higher commitments.

It _does not_ incentivize adding big chunks of new members, for example through a paid campaign, and is not susceptible to skew by small amounts of hyperactive members.

In other words, gravity is hard to hack.

Gravity is also universal, and it doesn't depend on community size, meaning that it can be compared across communities.

To learn how to calculate
and compare community sizes, see the [gravity + growth page](./gravity/growth).

## What's my community's gravity?

A community's field of gravity is like a fingerprint, traced out by the
imaginary curves that members traverse as their involvement goes up and down.

Learn how to [measure](./gravity/measure) and interpret gravity.
